On Wed, Nov 8, 2017 at 9:44 AM, Tom Herbert <t...@herbertland.com> wrote: > On Fri, Aug 18, 2017 at 3:27 PM, David Miller <da...@davemloft.net> wrote: >> From: Martin KaFai Lau <ka...@fb.com> >> Date: Fri, 18 Aug 2017 13:51:36 -0700 >> >>> It seems like that middle box specifically drops TCP_RST if it >>> does not know anything about this flow. Since the flowlabel of the TCP_RST >>> (sent in TW state) is always different, it always lands to a different >>> middle >>> box. All of these TCP_RST cannot be delivered. >> >> This really is illegal behavior. The flow label is not a flow _KEY_ >> by any definition whatsoever. >> >> Flow labels are an optimization, not a determinant for flow matching >> particularly for proper TCP state processing. >> >> I'd rather you invest all of this energy getting that vendor to fix >> their kit. >> > We're now seeing several router vendors recommending people to not use > flow labels for ECMP hashing. This is precisely because when a flow > label changes, network devices that maintain state (firewalls, NAT, > load balancers) can't deal with packets being rerouted so connections > are dropped. Unfortunately, the need for packets of a flow to always > follow the same path has become an implicit requirement that I think > we need follow at least as the default behavior. > > Martin: is there any change you could resurrect these patches? In > order to solve the general problem of making routing consistent, I > believe we want to keep sk_tx_hash consistent for the connection from > which a consistent flow label can be derived. To avoid the overhead of > a hash field in sk_common, maybe we could initially set a connection > hash to a five-tuple hash for a flow instead of a random value? So in > TW state the consistent hash can be computed on the fly. > Sorry, I failed to give credit to Shaohua for submitting the initial patch. Please take look!
> Tom
